Most surveillance cameras use a mechanically movable optical filter system that is constructed to selectively block focus-distorting wavelengths of light from impinging on the sensor of the camera. During daytime operation, in which there is strong ambient light, an optical filter passing visible light is mechanically positioned in front of the light sensitive surface of the sensor to reduce image-degrading focus distortion that would arise in response to incident infrared light. During nighttime operation, in which there is weak ambient light, an optical filter passing infrared light is mechanically positioned in front of the light sensitive surface of the sensor to enable use of infrared light to produce an image. A mechanized optical filter switching apparatus for use in an optical instrument is described in U.S. Patent Application Pub. No. US 2005/0141117 A1 of Kim et al.
What is needed is an optical shutter that, in absence of mechanical motion, selectively blocks NIR light wavelengths from reaching the sensor of the camera during daytime operation.